The present invention relates to vacuum treatment chambers for work pieces and for treatment methods using the same. In a preferred embodiment, a vacuum treatment chamber for work pieces comprises at least one induction coil for at least co-generating a treatment plasma in a discharge chamber which is located in the interior of the coil.
It is generally known in the art that plasmas can be generated inductively and/or capacitively in vacuum treatment chambers for work pieces.
In the context of capacitive plasma generation, electrodes that are envisioned inside the vacuum chamber are connected with different electric potentials, such as e.g. DC-or HF- potentials, which produces an electric field between the electrodes, similar to that of a capacitor that uses the vacuum as dielectric.
At least one induction coil is envisioned for the inductive plasma generation. The coil surrounds the plasma discharge chamber, and an induction field is generated inside the chamber.
As mentioned previously, frequently, the plasma undergoes a combination of capacitive and inductive excitement; in part this also applies for connected plasmas in which a virtual xe2x80x98stand by plasmaxe2x80x99 is inductively generated and the capacitively injected power is switched on and off.
To inductively inject the induction field into the discharge chamber it is possible for the induction coil to be exposed vis-a-vis the discharge chamber; but preferably it is separated from the latter by way of a dielectric wall, and is, for the most past, arranged positioned on the outside in relation to the vacuum chamber, or it is, if necessary, embedded in the material of the dielectric wall. A vacuum treatment chamber in which capacitive and inductive plasma generation are used in combination is known in the art from, for example, European Patent No. 0 271 341.
If electrically conductive particles are released inside a chamber, in which a plasma is inductively at least co-produced, such as e.g. during sputter-etching of electrically conductive work piece surfaces or during sputter-coating of work pieces with electrically conductive layers or during PECVD processes that produce electrically conductive particles, the problems described below occur.
If the induction coil is freely exposed to the discharge chamber inside the treatment chamber, there results the formation of an interference layer on the induction coil. With increasing duration of the process this leads to the chipping of particles from the interference layer followed by the corresponding impairment of the process.
If, as preferred, the induction coil is separated from the discharge chamber by way of a dielectric material, the result is that with increasing duration of the process an increasingly thick layer of electrically conductive material is formed on the dielectric wall. This reduces the power that was inductively injected into the discharge chamber and converts it increasingly to heat in the electrically conductive interference layer.
U.S. Pat. No. 5,569,363 addresses these problems that occur inside a sputter treatment chamber with capacitive high frequency and inductive plasma excitement using an induction coil that is arranged outside of a dielectric wall. To resolve the problem of the dielectric inside wall becoming coated with an interference layer consisting of electrically conductive material that patent envisions a cylindrical steel screen with a thickness of approximately 0.1 mm between the discharge chamber and the dielectric wall. The screen is continuously slotted parallel to the axis of the induction coil. This longitudinal slot prevents rotating circular currents from developing inside the metallic cylinder screen, because their path is interrupted by the slot. Also with respect to the deposition of electrically conductive layers on the inside wall of the cylinder this interruption remains effective. It is in fact the screen that protects the dielectric wall from becoming coated with electrically conductive particles. A disadvantageous aspect of this method is the fact that the inductive power injection is considerably reduced if a conductive screen such as this is envisioned.
Similarly, a vacuum treatment chamber is known in the art from European Patent No. 0 782 172 which provides, again in combination, that a plasma is generated capacitively by way of DC-operation of a target as well as inductively by way of HF-operation of an induction coil for the sputter-treatment of work pieces. In one embodied example the induction coil is located inside the vacuum recipient, and in the other embodied example the induction coil is embedded in the dielectric wall. At any rate, at least one cylindrical screen, consisting of a dielectric or a metallic material, is envisioned between the discharge chamber and the induction coil. The screen is equipped with at least one slot running parallel to the axis or with a few continuous slots that are distributed around the circumference of the screen dividing the screen into separate segments.
On the basis of U.S. Pat. No. 5,569,363 and European Patent No. 0 782 172 it is assumed that, irrespective of the fact whether the slotted screen is manufactured from a metallic or from a dielectric material, the electrically conducting interference layer is caught on the screen. Already a single slot will prevent the development of circular currents in the conductive interference layer; however, several evenly distributed slots will, obviously, help achieve better symmetry of the discharge conditions. To avoid that electrically conducting interference layers become deposited on the induction coil or on the dielectric wall because they penetrated through the slots of the one screen, a second coaxial screen is envisioned in accordance with EP-A, which is realized like the screen referred to previously, but the slots are offset at an angle in relation to the former screen.
It can be noted that irrespective of whether the screen is manufactured from a dielectric material or from metal its surface area that is directed toward the discharge chamber will become electrically conducting due to the electrically conducting interference layer.
On the basis of a vacuum treatment chamber for work pieces with at least one induction coil, which is intended to produce a treatment plasma, at least in part, inside a discharge chamber and is located inside the coil, as well as a slotted screen, which is located between the discharge chamber and the coil, in particular arranged in a coaxial direction in relation to the axis of the coil, and whose slots have a direction component that is parallel to the axis, in accordance with the vacuum chamber that is described in European Patent No. 0 782 172 it is the subject matter of the current invention to decisively neutralize the reduction of inductively injected power into the discharge chamber if an electric interference layer is on the screen and, at the same time, to reduce the down-time of the treatment chamber due to the exchange of interference-coated screens.
For now, irrespective of the fact whether the screen consists of metal or of a dielectric material, the present invention relies on the realization that if the inside surface of the screen is electrically conductivexe2x80x94at least if an electrically conductive interference layer is presentxe2x80x94it is in fact eddy currents that cause to a crucial degree of the losses of inductively injected power and notxe2x80x94at least not exclusivelyxe2x80x94circular currents, as outlined in particular in accordance with U.S. Pat. No. 5,569,369. Consequently, according to the invention the screen is equipped with a high slot density. This high density of slots can only be realized in a user-friendly fashion if the body that is used for the screen is self-contained, which, moreover, achieves the objective of allowing for a fast replacement of the screen.
In a preferred embodied example the selected slot density S (number of slots per cm) is
1xe2x89xa6S, preferably even
1.5xe2x89xa6S;
preferably the slot width d is
dxe2x89xa62 mm, preferably
dxe2x89xa61 mm.
The maximum limits for the slot density are derived from the limits prescribed by slot manufacturing and the minimum slot widths that must be observed to avoid, taking into consideration span of the serviceable life, that the narrowing of the slots caused by interference layers, depending on the respective interference layer material, occurs too quickly.
In a preferred example, the screen according to the invention is realized from metal and preferably connected with a reference potential, such as e.g. a ground potential. In contrast to a dielectric screen the metal screen has the advantage, among other advantages, that aside from the electrically conducting interference layer that is building up no other significant change of the inductively injected power results, which is why the preadjusted plasma density in accordance with the inductively injected power will not change much more due to the building interference layer. If the slots are offset in a radial direction, when looked at from a top view, i.e. if viewed in the direction of the axis of the coil, the protective effect of the screen is increased even further against any penetration from the interference layer.
In a particularly preferred embodied example the chamber has a coaxial wall consisting of dielectric material. The screen is located inside this wall and the induction coil is arranged inside or outside of this wall.
Another preferred embodied example provides that at least one pair of electrodes is envisioned inside the chamber, and the pair of electrodes is connected with a DC-source, an AC-source, an AC+DC-source, a pulsating DC-source, preferably an HF- or DC- source. The coil excites the operating plasma inductively and the electrode pair capacitively. Suitable as electrode or electrode pair can be a sputtering source, such as a magnetron source or a substrate support. Preferably, the induction coil is operated with a medium frequency generator that operates at medium frequency fm:
100 kHzxe2x89xa6fmxe2x89xa6800 kHz,
preferably
fm=approximately 400 kHz.
Even if the narrow-slotted screen envisioned according to the invention, whose slots do not have to be parallel to the axis but can also be arranged at an oblique angle with regard to this aspect, consists of metal, depending on the type of material during the build-up of the interference layer, a change with regard to the inductively injected power takes place. This occurs even more massively, if the screen according to the invention is manufactured from a dielectric material. In an effort to at least counteract these problems and in order to maintain the plasma""s operational conditions at a level that is as constant as possible or that involves intended time-related changes a measuring apparatus is envisioned on the treatment chamber according to the invention for the plasma density in one preferred embodied example; preferably this is a voltage measuring apparatus on an electrode, for example on a work piece support or on a sputtering target, whose starting signal is fed into the control circuit as a measured ACTUAL value, and the control circuit acts as a final control element on the generator for the induction coil.
In another embodied example the slotted screen according to the invention that is inside the vacuum chamber can be used to separate the discharge chamber from a circular chamber, which is arranged radially and outside and into which a gas line runs. Consequently, the screen and its slots are utilized also as a means to jet-feed the gas into the discharge chamber forming a slot ring jet apparatus. During reactive processes the inert working gas, such as argon, is preferably jet-fed through the screen referred to previously, a process that will additionally delay the effective layer buildup capacity with an electrically conductive interference layer.
The method according to the invention can be further used, in particular in connection with sputter-etching of metallic layers, sputter-coating of work pieces, such as e.g. of thin film head for magnetron-sputtering. As referred to previously, it can also be utilized for other plasma-supported treatment methods in which the plasma is, at least in part, inductively excited, such as in the context of PECVD processes and reactive sputtering-processes, such as sputter-coating or sputter-etching processes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.